Cerebral ischemia is a major cause of death and long-term disability, with high accompanying social and medical costs. Approximately 795,000 Americans suffer a stroke each year at an estimated annual cost of $73.7B (American Heart Association. Heart Disease and Stroke Statistics, 2010 Update). Substantial preclinical data support the use of NMDA receptor antagonists to reduce brain damage caused by cerebral ischemia. However, to date no drug acting through this target has been successful in clinical trials of cerebral ischemia, largely due to two issues: i) adverse effects that prevented attaining drug levels adequate for efficacy, and ii) clinical restraints that prevented drug administration within the short time after ischemia required for efficacy. We are using a multi-pronged strategy to overcome these obstacles in the development of a context-dependent, pH-sensitive, NR2B subunit selective NMDA receptor antagonist for prophylactic use in subarachnoid hemorrhage (SAH). SAH patients are at substantial risk of experiencing a stroke-like ischemic event four to 14 days after their surgery to coil or clip their aneurysm. NR2B selective antagonists are intrinsically better tolerated than early generations of non-selective NMDA antagonists. Furthermore, our medicinal chemistry and pharmacology group has discovered and optimized compounds selective for NR2B receptor inhibition that are more potent at the interstitial acidic pH characteristic of the penumbral region in focal ischemia than non-ischemic tissue. More importantly, the relative lack of NMDA receptor block in non- ischemic, healthy tissues at physiological pH minimizes the potential for on-target cognitive and psychotomimetic adverse effects that have limited prior drug candidates. Because of the context-dependent, penumbral-selective actions of our compounds, we anticipate a dramatic improvement in drug tolerability, allowing for prophylactic administration prior to ischemia during the 14 days after aneurysm surgery in SAH patients. Thus, our IND candidate will be available for neuroprotective NMDA receptor block at the site of, and earliest onset of, secondary ischemia. The work proposed here is aimed at identifying a novel neuroprotective agent suitable for prophylactic use by taking advantage of coupling pH-dependent receptor block with the intrinsic efficacy and tolerability of NR2B-selective NMDA receptor blockade.